Angiografia

Page 1

Pe d i a t r i c I m a g i n g • C l i n i c a l Pe r s p e c t i ve Young et al. MR Angiography of Congenital Cardiovascular Disease

FOCUS ON:

Downloaded from www.ajronline.org by Eric Maldonado Munoz on 10/22/13 from IP address 186.151.190.13. Copyright ARRS. For personal use only; all rights reserved

Pediatric Imaging Clinical Perspective

Tips and Tricks for MR Angiography of Pediatric and Adult Congenital Cardiovascular Diseases

Phillip M. Young1 Kiaran P. McGee Matthew S. Pieper Larry A. Binkovitz Jane M. Matsumoto Amy B. Kolbe Thomas A. Foley Paul R. Julsrud

OBJECTIVE. The use of contrast-enhanced MR angiography (MRA) as an alternative to CT angiography or conventional angiography to assess pediatric and adult patients with cardiovascular diseases has the potential to significantly reduce patients’ lifetime exposure to ionizing radiation. However, imaging this group of patients can be challenging because of a number of factors, including small size, difficulty timing the contrast bolus to the territory of interest, and the presence of metallic susceptibility artifact resulting from stents or clips. CONCLUSION. We present some suggestions to overcome many of these obstacles to MRA in these patients, highlighted with illustrations from clinical cases.

Young PM, McGee KP, Pieper MS, et al.

ontrast-enhanced MR angiography (MRA) is an attractive technique for noninvasive assessment of patients with pediatric and adult congenital cardiovascular diseases. The lack of ionizing radiation is a benefit of MRA in distinction to CT angiography (CTA) or conventional angiography for younger patients, because many such patients are serially imaged and will require lifetime follow-up, resulting in high cumulative radiation exposure. In addition, the ability to obtain a 3D dataset with wide anatomic coverage is an advantage of MRA over both conventional angiography and vascular ultrasound. Nevertheless, MRA can be challenging in these patients because of a number of specific issues. Younger patients often will not tolerate the MRA examination unless it is performed under general anesthesia, which entails its own risks [1]. In small children, obtaining adequate spatial resolution to depict cardiovascular pathologic abnormalities can be difficult. Smaller and younger patients are also difficult to image with MRA because it can be difficult to accurately time the contrast bolus to the territory of interest because of small bolus volume and rapid circulation time. Even in older children and adults who can be given larger contrast boluses, properly timing the scan delay from injection to highlight cardiovascular abnormalities can be difficult in the presence of shunting or postoperative anatomy, such as a Fontan circulation. Other challenges include

Keywords: congenital cardiovascular disease, CT angiography, MR angiography DOI:10.2214/AJR.12.9632 Received July 13, 2012; accepted after revision December 4, 2012. 1

All authors: Department of Radiology, Mayo Clinic, 200 First St SW, Rochester, MN 55905. Address correspondence to P. M. Young (young.phillip@mayo.edu).

AJR 2013; 200:980–988 0361–803X/13/2005–980 © American Roentgen Ray Society

980

C

the presence of implanted metallic stents and surgical clips. Existing and evolving MRA techniques have the potential to help overcome many of these limitations. Judicious use of parallel imaging, blood-pool contrast agents, and other specialized techniques can improve image quality, spatial resolution, and overall diagnostic utility significantly over conventional approaches. With proper attention to technique, MRA is a powerful tool that can successfully image a wide range of cardiovascular abnormalities. We will present some “tips and tricks” we use in clinical practice to approach imaging problems, with a focus on state-of-the-art techniques available on newer scanners. Parallel Imaging Parallel imaging techniques intentionally undersample k-space, decreasing the amount of time required to acquire a given imaging volume. Briefly, these techniques all exploit coil geometry and the sensitivities of individual elements in the coil array for different regions of the imaged volume to extrapolate spatial information in the image. By doing this, phase encoding can be undersampled, and the spatial aliasing that would normally occur can be “unwrapped” using coil sensitivity information, which is obtained either before [2, 3] or during [4] the diagnostic scan. For 3D acquisitions such as the 3D spoiled gradient-echo sequences used for MRA, there are two phase-encoding directions; thus, 2D acceleration techniques can

AJR:200, May 2013


Turn static files into dynamic content formats.

Create a flipbook
Issuu converts static files into: digital portfolios, online yearbooks, online catalogs, digital photo albums and more. Sign up and create your flipbook.